1. The Field of the Invention
The present invention relates generally to optical transceiver modules. More specifically, the present invention relates to molded lead frame connectors used to connect an optical sub-assembly to a printed circuit board in an optical transceiver module.
2. Background and Relevant Art
Optical transceivers are used to transmit and receive optical signals from an optical network and to enable electrical network components to interface with and communicate over optical networks. Many optical transceivers are modular and are designed in accordance with industry standards that define mechanical aspects of the transceivers, form factors, optical and electrical requirements, and other characteristics and requirements of the transceivers. For example the Small Form-Factor Module Multi-Source Agreement (SFF MSA), the Small Form-Factor Pluggable Module Multi-Source Agreement (SFP MSA) and the 10 Gigabit Small Form Factor Pluggable Module Multi-Source Agreement (XFP MSA) Revision 3.1 define such standards.
The basic optical components of conventional transceivers include a transmitter optical sub-assembly (TOSA) and a receiver optical sub-assembly (ROSA). The TOSA receives electrical signals from a host device via circuitry of the transceiver module and generates a corresponding optical signal that is then transmitted to a remote node in an optical network. Conversely, the ROSA receives an incoming optical signal and outputs a corresponding electrical signal that can then be used or processed by the host device. Additionally, most transceivers include a rigid printed circuit board (PCB) containing, among other things, control circuitry for the TOSA and ROSA.
The connections between the optical sub-assemblies and the PCB in the transceiver module have various electrical and mechanical requirements. For instance, it is desirable to match the impedances of the TOSA, ROSA, and/or the PCB to reduce and/or eliminate signal reflection and losses. One of the most common electrical connection components used in conventional optical transceiver modules is a flexible printed circuit board, or “flex circuit,” that connects the rigid printed circuit board to leads associated with the TOSA or ROSA. Flex circuits have several advantages, including good electrical performance and radio frequency response. Advantageously, the flex circuits also have the ability to take up tolerances in the modules and to withstand stresses that arise during manufacture and operation of the modules.
While flex circuits have been widely used in recent years in optical transceiver modules, flex circuits represent a significant portion of the costs and labor required to manufacture transceiver modules. As the price of transceiver modules drops, the costs associated with flex circuits continue to represent an increasing proportion of the overall costs of transceiver modules. Due to the nature of flex circuits, the costs of producing flex circuits are generally higher than the cost of a PCB that performs the same functions.
Other approaches to connecting optical sub-assemblies to printed circuit boards have been introduced in recent years. For example, the leads protruding from TOSAs and ROSAs can be bent into a configuration that enables the leads to be directly soldered or otherwise connected to the printed circuit board. This technique is often less expensive than the use of flex circuits, but can lead to unfavorable radio frequency (RF) response due to the inability to carefully control impedances. In addition, bending the leads of TOSAs and ROSAs introduces reliability risks due to the likelihood of damaging glass seals or other fragile portions of the header assemblies in TOSAs and ROSAs that enclose the lasers and photodetectors, respectively.
Because of the possibility of damaging the TOSAs and ROSAs and poor electrical performance, bending the leads of the TOSAs and ROSAs to enable them to be directly connected to the printed circuit board is not suitable for many transceiver modules. This approach is particularly unsuitable for relatively high-speed transceiver modules, in which the RF response of the conductors is more important.
In addition with general problems associated with connecting the OSAs and PCB, it is also necessary for the structure connecting the OSA and the PCB to impedance match with the OSA and the PCB. Although it is possible to design the OSA, connector, such as the flex circuit, and the PCB in their respective interfaces, sometimes it is necessary to operate the OSA at a different signal rate. With the frequency of the signal being related to impedances, changes in the OSA operating frequency result in changes to the matched impedances. This can degrade the signal because unmatched impedances result in signal reflections and signal losses. It is difficult for existing technologies to accommodate for changes in OSA usage without redesigning the OSA, PCB and the flex circuit, which is costly and time consuming.